Fibre-reinforced pressure vessel and method of manufacturing fibre-reinforced pressure vessel

ABSTRACT

The invention relates to a fibre-reinforced pressure vessel ( 1, 6 ) comprising a rigid gas- or fluid-tight body ( 2, 7, 13, 19 ) overwound with fibre filaments ( 3, 10, 11, 18 ), whereby the fibre filaments are wound such that at least a number of fibre filaments can freely move in respect of one another and when the pressure vessel is under internal pressure the fibre filaments are strained exactly in their longitudinal direction. The invention also relates to a method of manufacturing a fibre-reinforced pressure vessel whereby no matrix material (for example, resin) is used so that at least a number of fibre filaments would be incorporated in a matrix for that section of the pressure vessel in which the fibre filaments can freely move in respect of one another.

[0001] The invention relates to a fibre-reinforced pressure vesselcomprising a rigid gas- or fluid-tight body overwound with fibrefilaments. The invention also relates to a method of manufacturing afibre-reinforced pressure vessel comprising a rigid gas- or fluid-tightbody overwound with fibre filaments.

[0002] Known fibre-reinforced pressure vessels comprise a rigid gas- orfluid-tight body overwound with fibre filaments. During themanufacturing of fibre-reinforced pressure vessels fibre filaments areapplied in certain patterns, so that when the pressure vessel is underinternal pressure the fibre filaments can absorb tensile stresses. Priorto, during or after winding, a binder or resin (a so-called matrixmaterial) is applied to the body which is (to be) overwound or to thefibre filaments. After winding, the matrix material is cured so that thefibre filaments are incorporated in a matrix (the binder or resin). Infibre-reinforced pressure vessels the matrix serves to transfer shearstresses from one fibre filament to another or to the gas- orfluid-tight body when the pressure vessel is under internal pressure.Sometimes extra windings are applied to (sections of) the gas- orfluid-tight body in order to absorb mechanical loads resulting frominter alia shear stresses.

[0003] Known methods of manufacturing fibre-reinforced pressure vesselscomprise a solidification or curing step in order to incorporate thewound fibre filaments in a matrix. Curing takes time, usually 6 to 8hours.

[0004] A disadvantage of known pressure vessels and methods ofmanufacturing the same is the need for a solidification or curing stepwhich usually lasts 6 to 8 hours. Another disadvantage is that forabsorbing mechanical loads resulting from inter alia shear stressesextra windings are sometimes necessary.

[0005] It is an objective of the invention to provide an improvedpressure vessel. It is another objective of the invention to provide areduction of production costs of fibre-reinforced pressure vessels. Itis yet another objective of the invention to provide an improved methodof manufacturing fibre-reinforced pressure vessels.

[0006] According to a first aspect of the invention one or moreobjectives are achieved with a fibre-reinforced pressure vesselcomprising a rigid gas- or fluid-tight body overwound with fibrefilaments, whereby at least a number of fibre filaments can move freelywith respect to one another and the fibre filaments are wound such thatwhen the pressure vessel is under internal pressure the fibre filamentsare loaded exactly in their longitudinal direction.

[0007] Since the fibre filaments are wound such that, when the pressurevessel is under internal pressure, they are loaded only longitudinally,they will remain in place during use and a matrix will not be required.

[0008] It is further achieved that only just as much fibre materialneeds to be used as is necessary for exactly absorbing the mechanicalstresses in the pressure vessel. No extra fibre filaments are necessary,leading to a reduction in weight and to lower costs as compared to knownpressure vessels.

[0009] Since at least a number of fibre filaments can move freely withrespect to one another and the fibre filaments are wound such that whenthe pressure vessel is under internal pressure the fibre filaments areloaded exactly in their longitudinal direction, the fibre filaments inthat section of the pressure vessel will be displaced with respect toone another when the pressure vessel for example is damaged.

[0010] Preferably, the fibre filaments can move freely with respect toone another throughout the whole of the pressure vessel.

[0011] This is advantageous in that no matrix material (for example,resin) at all needs to be used. This makes a curing step superfluous andit leads to lower costs as compared to known pressure vessels.

[0012] Preferably, the pressure vessel according to the invention has anisotensoid shape, that is, a shape whereby when the pressure vessel isunder internal pressure the mechanical stresses are distributed equallyamong the fibre filaments. In order to provide the pressure vessel withthe desired isotensoid shape a means for axially strengthening thepressure vessel may be used.

[0013] Since an isotensoid shape is used, only a minimum number of fibrefilaments are needed in order to absorb the mechanical stresses in thepressure vessel.

[0014] Moreover preferably, the pressure vessel according to theinvention has a cylindrical shape which is provided with isotensoid endpieces at both longitudinal ends thereof.

[0015] By providing the pressure vessel with a cylindrical shape, it issuitable for use as a gas flask.

[0016] Preferably, the pressure vessel according to the invention isprovided with a protective layer, a so-called coating.

[0017] A coating comprising synthetic rubber is particularly suitable asa protective means against fire and against small impact and handlingloads.

[0018] Preferably, the rigid body of a pressure vessel according to theinvention is made of high-density polyethene (HDPE) and the fibrefilaments are carbon filaments.

[0019] This combination of materials is advantageous from the viewpointof production costs and the weight and strength of the pressure vessel.

[0020] Preferably, the rigid body of a pressure vessel according to theinvention is made of high-density polyethene (HDPE) and the fibrefilaments are glass fibres.

[0021] This combination of materials, too, is advantageous from theviewpoint of production costs and the weight and strength of thepressure vessel.

[0022] A pressure vessel according to the invention can be manufacturedin different embodiments and thus be made suitable for different maximuminternal pressures.

[0023] According to a second aspect of the invention one or moreobjectives are achieved through a method of manufacturing afibre-reinforced pressure vessel comprising a rigid gas- or fluid-tightbody overwound with fibre filaments, whereby the method of manufacturingcomprises the steps of:

[0024] a) providing a rigid gas- or fluid-tight body, fibre filamentsand a winding apparatus;

[0025] b) overwinding the rigid body such that at least a number offibre filaments can move freely with respect to one another and thefibre filaments are wound such that when the pressure vessel is underinternal pressure the fibre filaments are loaded exactly in theirlongitudinal direction;

[0026] whereby no matrix material (for example, resin) is provided suchthat the fibre filaments would be incorporated in a matrix for thatsection of the pressure vessel in which the fibre filaments can movefreely with respect to one another.

[0027] By this it is achieved that no more fibre material is used thanthat what is necessary for exactly absorbing the mechanical stresses inthe pressure vessel. This leads to a reduction of the costs ofmanufacturing of the pressure vessel.

[0028] Preferably, no matrix material at all is provided for in themethod according to the invention. By not providing for a matrixmaterial in the pressure vessel a curing step is made superfluous. Bythis a shortening of the production time is achieved with respect to thetime which would otherwise be needed for solidification or curing, whichusually is 6 to 8 hours.

[0029] The invention is illustrated by way of two embodiments of thepressure vessel and one embodiment of the method of manufacturing thepressure vessel with reference to the accompanying drawings.

[0030]FIG. 1 depicts a first embodiment of the pressure vessel accordingto the invention having an isotensoid shape;

[0031]FIG. 2 depicts a second embodiment of the pressure vesselaccording to the invention having a cylindrical shape;

[0032]FIG. 3 is an axial cross-section view of an end of the pressurevessel of FIG. 2;

[0033]FIGS. 4A and 4B depict cross-sectional views of an example of therigid body of a pressure vessel with fibre filaments abutting the rigidbody according to the invention; and

[0034]FIG. 5 depicts schematically the mechanical load on a fibrefilament in its longitudinal direction according to the invention.

[0035] Referring to the drawings the two given embodiments of thepressure vessel according to the invention are now described.

[0036]FIG. 1 depicts a first embodiment of the pressure vessel accordingto the invention. The pressure vessel (1) comprises a rigid gas- orfluid-tight body (2) having an isotensoid shape. There are fibrefilaments (3) wound around the rigid body (2). There is also anauxiliary means (4). In this example the auxiliary means (4) is a meansfor axially strengthening the pressure vessel (1). The auxiliary means(4) is provided with means (5), screw holes in this example, with whichan appendage (not shown) such as a closure member or a pressure valvecan be attached to the pressure vessel (1).

[0037]FIG. 2 depicts a second embodiment of the pressure vesselaccording to the invention. The pressure vessel (6) comprises a rigidgas- or fluid-tight body (7) having a cylindrical shape. The cylindricalbody (7) is provided with an end-piece (8) having an isotensoid shape;The cylindrical rigid body (7) is shown mounted on a rotation-axis (9)which is used for winding fibre filaments around the rigid body (7). Therigid body (7) has several filaments (10) overwound in thecircumferential direction of the rigid body (7) (so-called ‘hoopwindings’) and several filaments (11) overwound in the longitudinaldirection of the rigid body (7) (so-called ‘helical or polar windings’).

[0038] The rigid body may comprise a thin layer of metal, athermoplastic or thermo-setting material, provided that the materialmeets the safety specifications applicable for the substance to becontained in the pressure vessel.

[0039] The fibre material is preferably carbon fibre, but it can also beany other fibre type which can be subjected to tensile stresses, such asE-type, R-type or S-type glass fibre, p-aramide fibre, carbon fibre orfibres of polymers such as polyethene, polyester or polyamide.

[0040]FIG. 3 depicts an axial cross-section view of an end of thepressure vessel (6) according to FIG. 2. It shows an end (12) of thecylinder-shaped rigid gas- or fluid-tight body (13) and an auxiliarymember (14) bordering the rigid body (13). In this example the auxiliarymember (14) and the rigid body together provide the end (12) with anisotensoid shape. In this example there are also openings (15) and (16)in the axial direction of the pressure vessel (6). This embodiment alsodepicts how the rigid body (13) and the auxiliary member (14) togetherhave been overwound with a layer (17) of fibre filaments (which areshown schematically).

[0041]FIGS. 4A and 4B depict cross-sectional views of an example of thepositions of fibre filaments (18) lying against (abutting) the rigidbody (19) of a pressure vessel according to the invention. In thisexample the fibre filaments (18) are in a cubic closest packing. FIG. 4Balso shows a coating (20) which has been applied to the fibre filaments.

[0042]FIG. 5 depicts the load with respect to an arc (AD) of a fibrefilament when the pressure vessel is under internal pressure (f) and theresulting reaction force (F) of the arc (AD) of the fibre filament. Rrepresents the radius of the rigid body and dν represents the arc angle.The fibre filament, of course, also exerts a normal force on the rigidbody.

[0043] The following is a description of an example of the method ofmanufacturing—according to the invention—a fibre-reinforced pressurevessel comprising a rigid gas- or fluid-tight body overwound with fibrefilaments.

[0044] One first determines the function of the pressure vessel andselects the materials to be used for the pressure vessel. Next, onedetermines a design, that is, the shape of the apparatus includingparameters such as the volume and dimensions of the vessel the maximumallowable internal pressure, safety factors, and the dimensions of theoutflow openings in the pressure vessel. A suitable production processis also selected. According to the invention the process is winding withfibres (‘filament winding’). For this process one determines a windingpattern appropriate in regard of the shape of the pressure vesselwhereby in the winding pattern the fibre filaments are overwound suchthat at least a number of fibre filaments can move freely with respectto one another and when the pressure vessel is under internal pressurethe fibre filaments are loaded exactly in their longitudinal direction.The rigid body thereby is not to contribute to the absorption ofmechanical stresses resulting from the internal pressure. The rigid bodycan be manufactured according to any known method, for example a methodusing a mould and blow moulding or spray moulding or rotation moulding.Subsequently, the rigid body is mounted on a winding apparatus(‘filament winding machine’). After setting the controls of the windingapparatus the leading end of a filament to be wound is attached to therigid body, the rigid body is overwound and the end of the woundfilament is fastened. Sometimes the winding pattern is applied inseveral stages. In the case of a cylinder-shaped rigid body for example,filaments overwound in the circumferential direction (so-called ‘hoopwindings’) and filaments overwound in the longitudinal direction(so-called ‘helical or polar windings’) are, for example, appliedseparately. When applying filaments in the longitudinal direction(so-called ‘helical or polar windings’) first an auxiliary member ispositioned against the rigid body and then the auxiliary member is alsooverwound with fibre filaments. After the rigid body has been completelyoverwound, the pressure vessel is optionally provided with a coating,preferably of synthetic rubber. The pressure vessel is optionallyprovided with an appendage.

[0045] The fibres are applied by means of winding, so-called filamentwinding. Since the fibre filaments are overwound such that, when thepressure vessel is under internal pressure, they are loaded only intheir longitudinal direction, they will stay in position during use anda matrix will not be necessary. Preferably, no matrix material (forexample, resin) at all is provided.

[0046] The fibres are not impregnated or glued or fastened to the rigidbody, of course except for the leading end of the very first fibrefilament to be overwound. Attachment of the fibre filament can also takeplace by forming a knot in the fibre filament. Impregnation is usuallyunderstood to include partial or complete penetration of any matrixmaterial in or between the fibre filaments. Thus, in the pressure vesselaccording to the invention no matrix material penetrates in or betweenthe fibre filaments because no matrix material is used. Matrix materialis usually a resin, synthetic resin or an elastomer. Furthermore, therigid body can move freely with respect to the fibre filaments.

[0047] In the method according to the invention there is nosolidification or curing step at all, thus not prior to, during or afterwinding.

[0048] Optionally, a flexible or a rigid protective layer, a so-calledcoating, can be provided on top of the fibre filaments. This coating isfire-proof and not constructively supporting, and it serves only toprotect the fibre filaments against external influences such as cuttingor abrasive actions, chemicals and against the influence of humidity orlight. Provision of this coating is not essential for performing theprimary function of a pressure vessel, namely safe containment of asubstance under pressure.

[0049] The coating, if provided for, can be formed from an elastomer orit can comprise a rigid shell of metal or of a thermplastic orthermo-setting material. Preferably, the coating is made of syntheticrubber.

[0050] A pressure vessel according to the invention can be used inparticular for containing or transporting substances under pressure,Such as propane, butane, CNG (compressed natural gas), air, water andcryogen substances such as liquid nitrogen or liquid oxygen. Dependingon the substance to be contained or transported, a pressure vesselaccording to the invention can be manufactured for a working pressure of0-5 bar (for example for hot water in an expansion vessel), 0-10 bar(for example for liquid oxygen or liquid nitrogen or for propane gas orbutane gas or a mixture thereof in gas flasks intended for use inhouseholds and at ambient temperatures), 0-35 bar (for example forpropane gas or butane gas at elevated temperatures), 0-100 bar (forexample for LPG in fuel tanks intended for use in motor vehicles), 0-300bar (for example for CNG or compressed air), and 0-600 bar for cryogenicgas systems in space technology applications.

[0051] The invention described above has the impact of a breakthrough inthe field of winding technology, in particular by overcoming thetechnical prejudice that use of a matrix material such as a resin isessential for fibre-reinforced pressure vessels. The invention istherefore considered to have a broad scope and not to be limited to onlythe above-described embodiments.

1. Fibre-reinforced pressure vessel (1, 6) comprising a rigid gas- orfluid-tight body (2, 7, 13, 19) overwound with fibre filaments (3, 10,11, 18), whereby at least a number of fibre filaments (3, 10, 11, 18)can move freely with respect to one another and the fibre filaments (3,10, 11, 18) are wound such that when the pressure vessel is underinternal pressure, the fibre filaments (3, 10, 11, 18) are loadedexactly in their longitudinal direction.
 2. Fibre-reinforced pressurevessel (1, 6) according to claim 1, whereby all wound fibre filaments(3, 10, 11, 18) can move freely with respect to one another. 3.Fibre-reinforced pressure vessel according to claim 1 or claim 2,whereby the pressure vessel (1) has an isotensoid shape. 4.Fibre-reinforced pressure vessel according to claim 1 or claim 2,whereby the pressure vessel (6) has a cylindrical shape. 5.Fibre-reinforced pressure vessel according to any preceding claim,whereby the pressure vessel (1, 6) is provided with a coating (20). 6.Fibre-reinforced pressure vessel according to claim 5, whereby thecoating (20) comprises synthetic rubber.
 7. Fibre-reinforced pressurevessel according to any of claims 1-6, whereby the rigid body (2, 7, 13,19) is made of high-density polyethene (HDPE) and the fibre filaments(3, 10, 11, 18) are carbon fibres.
 8. Fibre-reinforced pressure vesselaccording to any of claims 1-6, whereby the rigid body (2, 7, 13, 19) ismade of high-density polyethene (HDPE) and the fibre filaments (3, 10,11, 18) are glass fibres.
 9. Fibre-reinforced pressure vessel accordingto any of claims 1-8, whereby the pressure vessel (1, 6) can withstand aworking pressure in the range of 0-5 bar.
 10. Fibre-reinforced pressurevessel according to any of claims 1-8, whereby the pressure vessel (1,6) can withstand a working pressure in the range of 0-10 bar. 11.Fibre-reinforced pressure vessel according to any of claims 1-8, wherebythe pressure vessel (1, 6) can withstand a working pressure in the rangeof 0-35 bar.
 12. Fibre-reinforced pressure vessel according to any ofclaims 1-8, whereby the pressure vessel (1, 6) can withstand a workingpressure in the range of 0-100 bar.
 13. Fibre-reinforced pressure vesselaccording to any of claims 1-8, whereby the pressure vessel (1, 6) canwithstand a working pressure in the range of 0-300 bar. 14.Fibre-reinforced pressure vessel according to any of claims 1-8, wherebythe pressure vessel (1, 6) can withstand a working pressure in the rangeof 0-600 bar.
 15. Fibre-reinforced pressure vessel according to any ofclaims 9-11, suitable for use as a gas flask for propane or butane or amixture thereof for household uses.
 16. Fibre-reinforced pressure vesselaccording to claim 12 or claim 13, suitable as a fuel tank, inparticular for LPG, for use in motor vehicles.
 17. Fibre-reinforcedpressure vessel according to claim 13 or claim 14, suitable as a fueltank for CNG or compressed air.
 18. Fibre-reinforced pressure vesselaccording to claim 14 suitable for use as a cryogenic gas system inspace technology applications.
 19. Fibre-reinforced pressure vesselaccording to any preceding claim, whereby the pressure vessel (1, 6) isprovided with an appendage, for example a closure member or a pressurevalve.
 20. Method of manufacturing a fibre-reinforced pressure vesselcomprising a rigid gas- or fluid-tight body overwound With fibrefilaments, whereby the method comprises the steps of: a) providing arigid gas- or fluid-tight body, fibre filaments and a winding apparatus;b) overwinding the rigid body such that at least a number of fibrefilaments can move freely with respect to one another and the fibrefilaments are wound such that when the pressure vessel is under internalpressure vessel the fibre filaments are loaded exactly in theirlongitudinal direction; whereby no matrix material (for example, resin)is provided such that the fibre filaments would be incorporated in amatrix for that section of the pressure vessel in which the fibrefilaments can move freely with respect to one another.
 21. Method ofmanufacturing according to claim 20, whereby no matrix material at allis provided.
 22. Mould for use in manufacturing a fibre-reinforcedpressure vessel according to claim 20 or claim 21.